Recently, with rapid development of industry and economy, as the spread of electric devices and electronic devices is rapidly increased, demands for stable power supply and high-quality power have been increased, and as a result, a use of a uninterruptible power supply (UPS) for stable power supply during a power failure has rapidly increased. The degradation of power quality due to a momentary power failure, voltage sag, and a harmonic wave causes huge economic losses to the industry. As a part for solving such a problem of power quality, in the UPS frequently used in the industry, most of reliability for a stable operation is secured with rapid development of a power electronic technology, but the degradation of the power quality during the power failure due to a defect of a battery for energy storage has often occurred.
Accordingly, the importance of a technology of a battery management system (BMS) for more effectively using and managing the battery has been increased. Particularly, the BMS needs to prevent overcharging and overdischarging and protect the battery by easily controlling a charging state or a discharging state of the battery.
Generally, since the battery has a very high energy density, in the case where the battery is overcharged at a predetermined voltage or more, if the overcharging is severe, a structure of a positive active material is broken or oxidation of electrolytes is accompanied, and if this case persists, the voltage is increased and the battery is exploded or ignited. Further, a lifespan is shortened, the risk of accidents exists due to an instable characteristic of the battery, and as a result, the deterioration of the entire reliability of the UPS is caused.
Referring to FIG. 1, a battery charging and discharging circuit in the related art is illustrated, and may control charging and discharging by using only one switch 11 connected with the battery in series on a charging and discharging path. As a result, the battery charging and discharging circuit in the related art blocks a charging current by opening the switch 11 when the overcharging occurs, thereby preventing overcharging. However, the discharging current cannot move due to the opening of the switch 11.
Further, the battery charging and discharging circuit in the related art blocks the discharging current by opening the switch 11 when the discharging occurs, thereby preventing the overdischarging. However, the charging current cannot also flow due to the opening of the switch 11.
Finally, in the existing method, there are problems in that the discharging may be required even during the overcharging and the charging may be required even during the overdischarging, and both the charging and the discharging are not performed.